Buffeting Active Control in Transonic Flow

Abstract

In transonic flow conditions, the shock wave / turbulent boundary layer interaction and flow separations, which induce flow instabilities, “buffet”, and then structure vibrations, “buffeting”, can have an important influence on the aerodynamic behavior of the aircraft. The “buffet” phenomenon appears at high lift coefficient when the Mach number or the angle of attack of the aircraft increases. This phenomenon limits aircraft flight envelope. The objectives of this study are to cancel or to decrease the aerodynamic instabilities (unsteady separation, shock position movement) due to this type of flow by an active control system. A new moving part located at the trailing edge of the wing, the “Trailing Edge Deflector”, designed at ONERA, is used to decrease these instabilities. It can be moved to different static positions or be driven by dynamic motions. Tests were performed in transonic 2D and 3D flow with models well equipped in unsteady pressure transducers. For high lift coefficients, a selected static position of the “Trailing Edge Deflector” increases the wing aerodynamic performances and delays the “buffet” onset. In 2D flow “buffet” condition, the “Trailing Edge Deflector”, driven by a closed loop active control using the measurements of the unsteady wall static pressures, can greatly reduce the “buffet”. In 3D flow “buffeting” conditions, the 2D flow control principle is available but some differences must be considered.